The present invention relates to a liquid crystal display device and a method for fabricating the same. More particularly, the invention relates to a liquid crystal display device and a method for fabricating the same which achieves a high aperture ratio by constructing a part of a black matrix by a color filter when the black matrix and a color filter are formed on a first substrate.
Generally, a liquid crystal display device is comprised of a first substrate and a second substrate which are disposed to face each other over a liquid crystal layer. On the first substrate, a black matrix, a color filter, a counter electrode, and the like are formed. On the second substrate, a plurality of gate signal lines and a plurality of source signal lines which are disposed so as to perpendicularly cross each other via a gate insulating layer, thin film transistors disposed at intersecting points of the plurality of gate signal lines and the plurality of source signal lines, pixel electrodes arranged in a matrix which are disposed in respective areas surrounded by the plurality of gate signal lines and the plurality of source signal lines, and the like are formed. The gate electrode of each thin film transistor is connected to the corresponding gate signal line, the source electrode is connected to the corresponding source signal line, and the drain electrode is connected to the corresponding pixel electrode.
In the liquid crystal display device, in order to increase the high brightness and good image quality of display pixels, there is an increasing demand of raising the aperture ratio of the liquid crystal display device, specifically, the aperture ratio indicative of the ratio between the pixel area and the pixel opening. Recently, for example, a liquid crystal display device having a high aperture ratio has been disclosed in U.S. Pat. No. 5,877,830 (cited document 1).
FIGS. 5A, 5B, and 5C show the configuration of the liquid crystal display device disclosed in the cited document 1. FIG. 5A is a plan view. FIG. 5B is a cross section taken along the line VB-VBxe2x80x2 in FIG. 5A. FIG. 5C is a cross section taken along the line VC-VCxe2x80x2 in FIG. 5A.
Shown in FIGS. 5A, 5B, and 5C are a first substrate (counter substrate) 51, a second substrate (active matrix substrate) 52, a liquid crystal layer 53, a black matrix (BM) 54, a color filter 55, a counter electrode 56, a first alignment layer 57, a gate signal line 58, a storage capacitor line 58f, a gate insulation layer 59, a thin film transistor (TFT) 60, a gate electrode 60G, a source electrode 60S, a drain electrode 60D, a source signal line 61, a transparent pixel electrode 62 formed by a transparent conductive layer (ITO), a contact hole 63, an insulating interlayer 64, a second alignment layer 65, a transparent conductive layer 66, and metal conductive layers 67a and 67b. 
The liquid crystal display device shown in FIGS. 5A, 5B, and 5C is comprised of the first substrate 51 and the second substrate 52 arranged so as to face each other over the liquid crystal layer 53. On the first substrate 51, the black matrix 54, the color filter 55, the counter electrode 56 disposed opposite to the transparent pixel electrode 62, and the first alignment layer 57 are sequentially formed. On the second substrate 52, the plurality of gate signal lines 58 which are disposed in parallel and the plurality of storage capacitor lines 58f each of which is disposed between the neighboring gate signal lines 58 and 58 are formed. Further, the gate insulating layer 59, the thin film transistor 60, the insulating interlayer 64, the transparent pixel electrode 62, and the second alignment layer 65 are sequentially formed. The gate electrode 60G of the thin film transistor 60 is connected to the corresponding gate signal line 58 via the metal conductive layer 67a, the source electrode 60S is connected to the corresponding source signal line 61 via the metal conductive layer 67b, and the drain electrode 60D is connected to the corresponding storage capacitor line 58f via the transparent conductive layer 66 and also connected to the corresponding transparent pixel electrode 62 via the contact hole 63 formed in the insulating interlayer 64.
In the conventional liquid crystal display device having the configuration, the black matrix 54 formed on the first substrate 51 side covers only the peripheral part of the pixel area including the transparent pixel electrodes 62 arranged in a matrix on the second substrate 52 side and the area which is not covered with the black matrix 54 is used as an effective display area, so that a high aperture ratio is obtained.
In the conventional liquid crystal display device, the black matrix and the color filter are formed by a process as described below.
(1) First, a black matrix pattern is formed on a glass substrate by the photolithography method.
(2) For example, a pigment dispersed photosensitive resin for a green filter in which one of the three pigments constructing the color filter, for example, green pigment is dispersed is applied on the glass substrate.
(3) By using a mask for forming a green color filter, only an area in which the green color filter is to be formed on the glass substrate is irradiated with exposure light to expose the photosensitive resin layer for green filter in the area.
(4) A non-exposed area of the exposed photosensitive resin layer for green filter is removed by a developing process, thereby completing the formation of the green color filter.
(5) Then, for example, a pigment dispersed photosensitive resin for a red filter in which another one of the three pigments constructing the color filter, the red pigment, is dispersed is applied on the glass substrate on which the green color filter is formed.
(6) After that, by a process similar to the process of forming the green color filter, a red color filter is formed.
(7) A photosensitive resin for a blue filter, in which the last one of the three pigments of color filters, that is, blue pigment is dispersed is applied on the glass substrate on which the green and red color filters are formed.
(8) A blue color filter is formed by a process similar to that of forming the green color filter.
The liquid crystal display device disclosed in the cited document 1 has the following problems. Since the aperture ratio is specified by the gate signal lines 58 and the source signal lines 61 surrounding the transparent pixel electrodes 62, it is necessary to shield the area in which a thin film transistor is formed from incident light by using a metal mask newly formed via an organic insulating layer. Since the black matrix 54 is not disposed in the display area, the reflectance for ambient light increases and the contrast is lowered. Reflection light from the metal mask in the part in which the thin film transistor 60 is formed is observed from a gap of color patterns of the color filter 55 and displayed image non-uniformity such that an image changes irregularly according to a viewing angle occurs.
In a liquid crystal display device in which metal chromium (Cr) is used as a material of the black matrix, the manufacturing cost of the black matrix itself is as high as twice or more as compared with that of an ordinary black matrix using a black resin as a material of the black matrix. Consequently, there is a problem that the manufacturing cost of the liquid crystal display device is high.
On the other hand, in the case of a general color filter, although the black matrix using a black resin is cheap, not only the resolution of a display image is inferior, but also it is difficult to stably form the black matrix having a width of 10 xcexcm or narrower. The minimum black matrix width which can be stably formed at present is about 20 xcexcm.
It is therefore an object of the invention to provide a liquid crystal display device capable of obtaining a high aperture ratio with a simple configuration and a method of fabricating the same.
Another object of the invention is to provide a liquid crystal display device capable of obtaining a preferable image and a method of fabricating the same.
Further another object of the invention is to provide a liquid crystal display device which is fabricated at low cost and does not deteriorate the environment at the time of fabrication and a method of fabricating the same.
In order to achieve the objects, according to the invention, there is provided a liquid crystal display device comprising: a first substrate serving as a counter substrate; a second substrate serving as an active matrix substrate; and a liquid crystal layer provided between the first substrate and the second substrate, wherein a black matrix to be formed on the first substrate is constructed by a black resin optical shielding layer (black matrix film) and a blue filter layer.
According to the invention, there is provided a method for fabricating a liquid crystal display device, comprising: a first step of forming a black resin optical shielding layer in a predetermined part on the first substrate; a second step of sequentially forming a green filter layer and a red filter layer in predetermined parts on the first substrate; a third step of forming a photoresist film by applying a photoresist in which a pigment for forming the blue filter layer is dispersed on the first substrate; a fourth step of exposing the photoresist by irradiating the photoresist applied side with front side exposure light by using a photomask; a fifth step of exposing the photoresist by irradiating the front side of the first substrate which is opposite to the photoresist applied side with back side exposure light by using a frame-shaped photomask; and a sixth step of forming a blue filter layer by removing the non-exposed area of the photoresist.
In the liquid crystal display device according to the invention, the black matrix on a metal mask contributing to the aperture ratio of the liquid crystal display device is formed by the blue filter layer and the black matrix in the other part is formed by the black resin optical shielding layer. Consequently, the liquid crystal display device of a high aperture ratio with no deterioration in the image resolution can be obtained. Since the black resin optical shielding layer which is cheap is also used, the manufacturing cost can be suppressed to be low. Since no metal chromium is used, the environment is not deteriorated. Also in the case of using the blue filter layer as a material of the black matrix, reflection light from the metal mask can be sufficiently checked by the blue filter layer.
In the method for fabricating the liquid crystal display device, since both of the front side exposure and back side exposure are used at the time of forming the black matrix on the metal mask contributing to the aperture ratio of the liquid crystal display device by the blue filter layer, the blue filter layer constructing the color filter and the blue filter layer constructing the black matrix can be effectively formed. Simultaneously, the tolerance of optical leakage of the liquid crystal display device can be widened by a self alignment function.
Other objects, configurations, and effects of the invention will become more apparent as the following detailed description of embodiments proceeds.